A Study of Dynamics of Changes in Parameters of the Chandler Pole Oscillation in the Period 1975.0–2011.0

Abstract

A structural analysis of the time series of pole coordinate changes (version C01 IERS) for the period of 1975.0–2011.0 has been performed based on the nonlinear least squares method. Average estimates of the parameters of the main components of the pole movement—namely, Chandler, annual, and semiannual wobbles—are obtained for this period. The obtained values of periods T and amplitudes A of the main components are as follows: T = 433.49 ± 0.22 days and A = 160 ± 3 mas for the Chandler oscillations; T = 365.19 ± 0.37 days and A = 93 ± 5 mas for the annual oscillations; and T = 183.03 ± 0.34 days and A = 4 ± 2 mas for the semiannual oscillations. Changes in the pole coordinates are examined in the time series when focusing on the manifestation of Chandler oscillations. The dynamics of oscillation parameters (including amplitude, period, phase, and Q factor) is studied. Changes in the Chandler oscillation parameters show their interdependence. The correlation coefficient between phase and period variations is +0.94, and a similar relationship is observed between phase and amplitude variations with a correlation coefficient of +0.88. It is shown that the phase change precedes the changes in the amplitude and in the period. This behavior of the parameters of the Chandler wobble suggests that changes in the period and in the amplitude should be considered a consequence of the phase changes. It is revealed that an increase in the amplitude of Chandler oscillations correlates with a decrease in the attenuation decrement with a correlation coefficient of –0.98. These findings align with the statistical patterns articulated by Melchior, which are indicative of (a) inconstancy of the period of Chandler oscillations over time and (b) proportional changes between the period and the amplitude of oscillations. Thus, preference should be given to the one-component complicated model of the Chandler pole movement with a variable period for the studied period of time.